Hello vasagan,
Thank you for contacting us. We are happy to help, but will need more information to troubleshoot further, such as one of the email addresses that is experiencing a problem.
If emails are being bounced back/returned I recommend using our Bounce Back Parser, which can provide more details on the bounce, and allows you to easily submit a ticket to Live Tech support.
If you have any further questions, feel free to post them below.
Thank you,
-John-Paul